This invention relates generally to electric current detectors and more particularly, to a ground fault detector circuit for controlling the operation of a system connected thereto upon the occurence of a leakage of electric current or upon an input signal from a fire extinguisher system. The ground fault and fire detector circuitry of this invention has numerous applications and can be particularly used in industrial or commercial plants, manufacturing facilities, restaurants, kitchens, workshops, basements, assembly lines, public buildings, and virtually any other facility where a hazardous condition could arise due to a ground fault.
It is commonly known that a ground fault results when a failure in an electrical circuit permits leakage current or fault current to flow therein from a hot wire to ground. Such ground faults occur for many reasons such as for example, from worn insulations, the presence of moisture, deterioration in equipment from age or abuse, and from line to line short circuits in power lines.
Generally, it has been encountered that such leakage current can likewise exist between a ground on equipment and other electrical devices in industrial facilities, plants, and the like, and the earth ground. Particularly, when a ground fault occurs, a potentially hazardous condition can be created by which personnel in certain work areas may receive a sudden electrical shock upon contact with the electrical equipment in those areas. Another problem exists when a fire condition arises in the vicinity of the equipment necessitating disconnecting of power lines to minimize serious injury and damage.
In previous electric current detector circuits, failures of the devices were encountered when the fault or leakage current exceeded the specifications of the circuitry which would occur when the fault current reached a level of approximately three hundred amperes, a condition which could occur in actual practice.
It would therefore, be desirable to provide an electric current detector circuit which will both dependably and efficiently sense the presence of a leakage current over an increased range of values or the presence of a fire and thereby provide a signal to the electrical system connected thereto, to disconnect the power lines from the electrical system.